Many structures, such as buildings, and systems, such as aircraft, contain some type of smoke or fire detection system that detects smoke or fire, and thereafter provides an indication that a fire may exist within the structure or system. In many structures or systems, such smoke or fire detection systems include a plurality of smoke or fire detectors installed within a particular enclosure. In the context of aircraft, for example, the enclosure is typically a cargo or baggage compartment requiring numerous smoke or fire detectors.
Many regulatory authorities place limits on the amount of smoke allowed to exist in a structure or system before being detected by an appropriate smoke or fire detection system. In the context of aircraft, for example, the Federal Aviation Administration (FAA) has imposed limits on the amount of smoke allowed to exist undetected in many portions of aircraft. In addition, the FAA over time has reduced limits on the amount of time allowed for a smoke or fire detection system to detect a fire in many portions of aircraft.
Conventionally, improving detection performance of smoke or fire detection systems requires increasing the number of smoke or fire detectors, reducing the ventilation in the affected areas of the aircraft and/or increasing the sensitivity of the smoke or fire detectors. And whereas each technique for improving detection performance of smoke or fire detection systems is adequate, each has drawbacks. Increasing the number of fire detectors, for example, increases system costs associated with new detectors, as well as new electrical power sources, wiring, flight deck messages, plumbing complexity, and cargo liner and structural interfaces. Reducing ventilation potentially results in financial losses to the aircraft operator in that to reduce the ventilation, the quantity of some cargo types must typically be reduced, thus reducing the capacity of the affected area and the overall aircraft.
While increasing the sensitivity of the smoke or fire detectors will increase system performance, the number of false alarms initiated by the smoke or fire detectors will also increase. In this regard, the frequency of false alarms is often considered one of the biggest problems with conventional smoke or fire detection systems. Increasing false alarms, in turn, decreases system reliability and can impose considerable costs for the aircraft operator and can result in unnecessary bodily injury to passengers. False alarms can be generated when nuisance sources such as dust, moisture, and/or gasses, are presented to a detector at a level exceeding the alarm threshold. And whenever a fire alarm is triggered on an aircraft, for example, the aircraft crew typically discharge fire extinguishers in the affected area, divert the aircraft to the nearest airport, and occasionally initiate an emergency evacuation of the aircraft. Increased exposure to the number of false alarms results in the airlines incurring costs associated with replacing expended fire extinguishers, accommodating inconvenienced passengers and dispatching the aircraft from an unplanned destination. In addition, unnecessary emergency evacuations can result in unnecessary passenger injuries, which can occur during emergency evacuations.
To address the drawbacks associated with false alarms, conventional smoke or fire detection systems often impose dual-loop operation, requiring at least two detectors (out of the plurality of detectors included within a particular enclosure) to reach full alarm threshold before providing a fire alarm signal. Although this does provides a reduction in the number of false alarms, if any detector among the plurality of detectors fails and becomes inoperative, such systems revert to single-loop operation whereby an alarm signal is provided when a single detector reaches full alarm threshold. In this situation, however, the possibility of false alarms will increase.
Accordingly, there is a need for a smoke or fire detector system which reduces the likelihood of a false alarm even when a single detector fails and becomes inoperative.